| 摘要 |
PURPOSE:To prevent the user from failing to hear emergency siren souns, by providing a controlling circuit, which reduces the output according as the input signal of an LPF is increased, between an auxiliary input terminal and a mixing circuit in the interphone device provided on, for example, a motor cycle. CONSTITUTION:Input signals of auxiliary input terminals 1 and 1 to which sound output apparatus such as a radio can be connected and sound signals of microphones 2 and 2 are given to mixing circuits 5 and 5, and headphones 7 and 7 are connected to circuits 5 and 5 through head amplifiers 6 and 6. LPFs 8 and 8 which attenuate the high sound band such as siren sounds of emergency vehicles, a mixing circuit 9 for input signals of terminals 1 and 1, a buffer amplifier 10, and a rectifying circuit 11 are provided between terminals 1 and 1 and circuits 5 and 5, and FETs 12 and 12 are connected in parallel to LPFs 8 and 8, and the output of the circuit 11 is given to gates of FETs 12 and 12. Thus, siren sounds of emergency vehicles or the like are heard without hindrance practically even if input signals of auxiliary input terminals are high comparatively, and the normal service is possible. |
